Conventionally, an active matrix-type liquid crystal display device having a TFT (Thin Film Transistor) as a switching element is known. The liquid crystal display device includes a liquid crystal panel constructed by two insulating substrates which face each other. On one of the substrates of the liquid crystal panel, gate bus lines (scanning signal lines) and source bus lines (video signal lines) are provided in a lattice shape, and TFTs are provided near the crossing points of the gate bus lines and the source bus lines. The TFT is configured by a gate electrode, a source electrode, and a drain electrode. The gate electrode is connected to the gate bus line, the source electrode is connected to the source bus line, and the drain electrode is connected to any of pixel electrodes disposed in a matrix on the substrate for forming an image. On the other substrate of the liquid crystal panel, electrodes (hereinafter, referred to as “common electrodes”) for applying voltage across the pixel electrodes are provided. By the pixel electrode and the common electrode, a liquid crystal capacitance is formed. In such a liquid crystal display device, to sequentially select the gate bus line one-horizontal-scanning-period by one-horizontal-scanning-period, application to each gate bus line of an active scanning signal is repeated using one vertical scanning period as a cycle. Consequently, charges accumulated in each liquid crystal capacitance have to be held for approximately one vertical scanning period. However, the accumulated charges cannot be held only by the liquid crystal capacitance, so that auxiliary capacitance is provided in parallel with the liquid crystal capacitance. Note that, a group of components for forming one pixel including the above-described TFT, pixel electrode, common electrode, and liquid crystal layer will be referred to as a “pixel formation portion” in the following description. A group of pixel formation portions disposed in a matrix will be referred to as a “pixel matrix”.
In such a configuration, by applying a voltage corresponding to the value of a pixel corresponding to a pixel electrode, between the pixel electrode and the common electrode, and changing the transmittance of the liquid crystal layer in accordance with the voltage application, an image is displayed on the liquid crystal panel. On this occasion, to prevent deterioration in a liquid crystal material constructing the liquid crystal layer, the liquid crystal panel is AC driven. Specifically, a video signal (a drive video signal) is applied to a source-bus line so that the polarity (positive/negative) of the voltage applied between each pixel electrode and the common electrode is inverted, for example, frame by frame.
Generally, in an active matrix-type liquid crystal panel, since the characteristics of a switching element such as a TFT or the like provided for each pixel are insufficient, even when the positive and negative polarities of a drive video signal applied to a source bus line (application voltage using the potential of the common electrode as a reference) are symmetrical, the transmittance of the liquid crystal layer for positive data voltage and that for negative data voltage are not perfectly symmetrical. Consequently, in the driving method (frame inversion driving method) for inverting the positive/negative polarity of a voltage applied to the liquid crystal frame by frame, flicker occurs in display in a liquid crystal panel.
As a countermeasure against the flicker as described above, a driving method (line inversion driving method) for inverting the positive/negative polarity frame by frame while inverting the positive/negative polarity of an application voltage every horizontal scanning period is known. FIG. 37 is a plan view showing the configuration of a part of a general display unit in a liquid crystal display device employing the line inversion driving method. FIG. 38 is an equivalent circuit diagram showing the configuration of a part of the display unit in the liquid crystal display device. As shown in FIGS. 37 and 38, pixel formation portions each including a TFT, a pixel electrode, and the like are provided in correspondence with crossing points between gate bus lines Gn, G(n+1), G(n+2), . . . and source bus lines Sm, S(m+1), S(m+2), . . . . The auxiliary capacitance electrode (auxiliary capacitance line) Cs for forming auxiliary capacitance is provided as shown in FIGS. 37 and 38.
In the configuration as described above, a signal waveform chart in the liquid crystal display device employing the line inversion driving method is as shown in FIG. 39. As shown in FIG. 39, in each horizontal scanning period, all of the polarities of drive video signals applied to the source bus lines are the same. Moreover, the polarity of the drive video signal is inverted every horizontal scanning period. Further, the polarity of the drive video signal is inverted also frame by frame. Consequently, a polarity diagram (a diagram showing polarities of voltages (pixel voltages) applied to the liquid crystals in the pixel formation portions) in two frame periods is as shown in FIG. 40.
However, according to the line inversion driving method, suppression of flicker is insufficient. Consequently, a driving method (dot inversion driving method) of inverting the polarity of the pixel voltage by frame period and also inverting the polarities of pixels neighboring in the vertical (perpendicular) direction and the polarities of pixels neighboring in the lateral (horizontal) direction in one frame period is often employed. The signal waveform chart in the liquid crystal display device employing the dot inversion driving method is as shown in FIG. 41. Consequently, a polarity diagram in the 2-frame period is as shown in FIG. 42. As shown in FIG. 42, the polarities of the pixels neighboring in the vertical and horizontal directions become opposite to each other, so that flicker is effectively suppressed more than that in the line inversion driving method.
In FIGS. 39 and 41, attention is paid to changes in the potential Com of the common electrode. As shown in FIG. 39, in the line inversion driving method, the potential Com of the common electrode is inverted every horizontal scanning period (such a method is referred to as “opposite AC driving”). On the other hand, as shown in FIG. 41, in the dot inversion driving method, the potential Com of the common electrode is constant (such a method is referred to as “opposite DC driving”). When the opposite AC driving and the opposite DC driving are compared, the amplitude of the drive video signal in the opposite DC driving has to be made larger. Consequently, in the case of employing the opposite DC driving, a source driver having a large withstand voltage is required and power consumption becomes large. Note that, the potential Cs of the auxiliary capacitance electrode also changes like the potential Com of the common electrode in both of the line inversion driving method and the dot inversion driving method.
According to the invention of the liquid crystal display device disclosed in Japanese Unexamined Patent Publication No. 04-360127, an array of pixels is as shown in FIGS. 43 and 44. In the liquid crystal display device, two gate bus lines are provided so as to sandwich, from the upper and lower sides, the pixel formation portions included in each of rows of the pixel matrix. Two pixel formation portions are provided in a region surrounded by two source bus lines which are neighboring and two gate bus lines disposed on the upper and lower sides of each row. In the pixel formation portion disposed on the left side out of the two pixel formation portions, the source terminal of a TFT is connected to the source bus line disposed on the left side out of the two source bus lines, and the gate terminal of the TFT is connected to the gate bus line disposed on the upper side out of the two gate bus lines. On the other hand, in the pixel formation portion disposed on the right side out of the two pixel formation portions, the source terminal of a TFT is connected to the source bus line disposed on the right side of the two source bus lines, and the gate terminal of the TFT is connected to the gate bus line disposed on the lower side out of the two gate bus lines.
In the configuration as described above, when signals are outputted as shown in FIG. 45, the polarity diagram in two frame periods is as shown in FIG. 46. Specifically, display similar to that in the frame inversion driving method is performed. Moreover, when signals are outputted as shown in FIG. 47, the polarity diagram in two frame periods is as shown in FIG. 48. Specifically, in one frame period, display is performed in which the polarities of pixels neighboring in the lateral direction are opposite to each other. Further, when signals are outputted as shown in FIG. 49, display similar to that in the line inversion driving method is performed as shown in FIG. 40. Further, when signals are outputted as shown in FIG. 50, display similar to that in the dot inversion driving method is performed as shown in FIG. 42.
In the configuration disclosed in Japanese Unexamined Patent Publication No. 04-360127, although the number of gate bus lines is twice as many as that in the conventional general configuration as described above, the number of source bus lines is the half. Since the source driver is generally more expensive than the gate driver, the cost is reduced with this configuration.
According to the invention of the liquid crystal display device disclosed in Japanese Patent Publication No. 3504496, an array of pixels is as shown in FIG. 51. In the liquid crystal display device, the positional relation (connection relation) of a TFT included in each of the pixel formation portions, a source bus line, and a gate bus line vary among regions expressed by reference numerals Ga1 to Ga4 in FIG. 51. In such a configuration, the waveforms of signals in predetermined successive periods are as shown in FIGS. 52 and 53. In the period shown in FIG. 52, an active scanning signal is supplied only to the gate bus line disposed on the upper side of each row. In the period shown in FIG. 53, the active scanning signal is supplied only to the gate bus line disposed on the lower side of each row. In other words, in this configuration, interlace driving is performed. Note that, Japanese Patent Publication No. 3091300 also discloses an invention of a liquid crystal display device in which an array of pixels is different from the conventional general configuration.    [Patent Document 1] Japanese Unexamined Patent Publication No. 04-360127    [Patent Document 2] Japanese Patent Publication No. 3504496    [Patent Document 3] Japanese Patent Publication No. 3091300